Insights into the origin of a Mediterranean biodiversity hotspot based on palynological and biomarker analyses of Lake Ohrid sediments from Early Pleistocene (> 1.2 Ma)

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Mediterranean hotspots of plant diversity, such as the Ohrid region at present, are commonly associated with southern glacial tree refugia. Existing paleobotanical evidence suggests that SW Balkans have sheltered temperate tree populations over the last five climatic cycles. This project aims to use high-resolution palynological, charcoal and lipid biomarker analyses to study the origins of plant biodiversity at a southern refugium and to reconstruct the response of aquatic and terrestrial ecosystems to climate variability over the Early Pleistocene within the Ohrid Basin. Our current knowledge about EarIy Pleistocene climate and flora in the Mediterranean region is based mostly on fragmentary terrestrial archives complemented by marine cores. In an effort to improve our understanding of the climate and flora evolution over this interval, a new 550m-long core was retrieved in 2013 within the ICDP drilling at Lake Ohrid. Preliminary geochemical, pollen and diatom analyses show continuous sedimentation over the last 1.36 million years and indicate major shifts in organic carbon, pollen and diatom assemblages corresponding to the characteristic marine isotope stage (MIS) stratigraphy. Considering the reduced global ice volume and shorter climatic cycles paced by obliquity observed in marine cores during this period, the research objectives of this proposal are: (i) the determination of the floristic diversity in a southern refugium during the formation of Lake Ohrid and prior to the onset of the Mid- Pleistocene transition with a focus on relict subtropical species, (ii) the reconstruction of environmental and hydrological changes in the Ohrid Basin leading to the formation of the lake, (iii) the identification of the main drivers of terrestrial and aquatic ecosystem change in the Ohrid Basin since the formation of the lake under an obliquity-controlled climate regime (41-kyr cycles) between MIS 43 and MIS 35, and (iv) the quantitative reconstruction and assessment of the nature and amplitude of climate variability between MIS 43 and MIS 35 in the Eastern Mediterranean region. These objectives will be addressed in three work packages that will deliver the first highly-resolved pollen and non-pollen palynomorph and charcoal record, a lipid biomarker inventory of fluvial, peatland and lacustrine phases, as well as the first pollen- and biomarker-derived quantitative climate reconstructions for the Early-Pleistocene in the study region. Complementary tephrochronological, sedimentological, geochemical and diatom analyses over the same interval will provide independent age control points and will refine our understanding of changes in lake hydrology driving aquatic organism community turnovers.